Do Low Fat Diets Reduce Breast Cancer?

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About 25 years ago, Dr. Carroll published data that found a strong correlation between the amount of fat in the diet in different countries and the risk of developing and dying from breast cancer.

In the United States today, one out of every eight women will be diagnosed with breast cancer at some point in their life. More than 180,000 women will be diagnosed with breast cancer this year.

However, the relationship between dietary fat intake and breast cancer has remained controversial because data from the large Nurses’ Health Study has failed to find any connection between dietary fat intake and the risk of developing breast cancer even though this same study found a fairly strong association between increased dietary fat and a greater risk of colon cancer. Dr. Walter Willett at Harvard is one of the lead researchers in the Nurses Health Study. He has argued that the data he has published refutes the notion that dietary fat promotes breast cancer despite the fact that data in animals clearly shows that high-fat diets promote breast cancer.

Asian women who have consumed a diet low in fat and animal products typically have had a breast cancer death rate 75% to 90% lower than women in the U.S. Research has shown that when Asian women migrate to the U.S. their risk of breast cancer roughly doubles in about 10 years. By the second generation their daughters have about the same risk of developing breast cancer as other Americans, so it is hard to argue the low risk of breast cancer in Asian countries is due to genes. We also know that breast cancer rates are rising dramatically in Japan and Singapore as the amount of fat and meat in their diet has increased.

No one knows how a diet higher in fat promotes breast cancer. It is possible the risk of breast cancer from eating more fat occurs before women reach middle age. The Nurses’ Health study dealt with women middle-aged and older. Diets high in fat early in life often promote weight gain, particularly in inactive women. This leads to earlier menarche. Early menarche is a major risk factor for the development of breast cancer. High-fat diets can also increase insulin and insulin-like growth factor-1 (IGF-1) levels. Higher IGF-1 appears to promote breast and other cancers. High-fat diets are typically more calorie dense and lower in fiber than higher carbohydrate diets. Exercise lowers insulin and IGF-1 and women who are active early in life have been shown to have a reduced risk of developing breast cancer before menopause.

 

New Study Shows Cutting Fat Cuts Breast Cancer

Data from a new study of more than 2,400 post-menopausal women who had been treated successfully for early breast cancer suggests dietary fat may play some role in promoting breast cancer in older women as well. After a lumpectomy, these women at high risk of breast cancer were randomly assigned to either follow their usual diet or adopt a low-fat diet.

After 10 years of follow up, the results presented at the American Society for Clinical Oncology’s annual meeting in May, showed those who had been advised to adopt a low-fat diet (about 20% of calories) significantly reduced their risk of developing breast cancer compared to those consuming a diet with close to 30% fat.

Since data from a controlled clinical trial is generally more predictive of clinical benefit than epidemiological data, such as that gathered in the Nurses’ Health Study, it now seems clear that all women at high-risk of breast cancer should be advised to adopt a low-fat diet.

Another recent study published in the May 25th issue of JAMA showed that women with breast cancer cut their risk of dying from breast cancer if they were more active.

Since alcohol consumption has been consistently shown to elevate the risk of breast cancer, women at high risk of breast cancer should be discouraged from having more than an occasional drink.

By James J. Kenney, PhD, RD, FACN.

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